You can use Alt+[number] to switch to the tab numbered [number] on Linux, but I always lose track of which tab is which after about the third one, which kind of defeats the purpose. With this extension I don't need to count from the left.
It doesn't sound that useful just reading it, but I'd recommend trying it out a bit. Can be useful if you're like me and switch between tabs a lot!
Great concept, and useful for very small sessions, but I rarely have only 9 tabs open. This should be able to handle input like "cmd-3-2" (or "ctrl-3-2"), as long as either the modifier key is still held down, or the keystrokes are entered within 1 second, either way you want to implement it.